1. Field of the Invention
This invention relates to an injection device and in particular to a hydro-pneumatic jet injector for administering medicine through the skin of humans or animals without the use of skin-piercing needles.
2. Discussion of the Prior Art
Jet injection devices of the type disclosed herein have met limited acceptance because of the high pressures required to perforate the skin of humans or animals. Such high pressure has been achieved thus far by various means, including explosives, hydraulic pumps, carbon dioxide cylinders and springs. However, several problems have been encountered with jet injectors.
Instruments using explosive materials are definitely dangerous and their use is not recommended. Hydraulic devices require heavy equipment, such as pumps, high pressure tubing and hydraulic controls, which are not only cumbersome but also expensive. Small carbon dioxide cylinders are well suited for portable instruments, but it is very difficult with such instruments to obtain the constant pressure needed to control the dose of medicine to be injected. It will be appreciated that control of the dose of medicine is most important. Moreover, such a device requires storing of an adequate supply of carbon dioxide cylinders. Other pneumatic instruments employ gas bottles or gas reservoirs and high pressure tubing. Such equipment is, however, bulky and not portable.
The most commonly used instruments are operated by steel springs. However, for the usual doses of 1.0 ml springs having long strokes are needed, due to the inherent characteristic of compressed springs to lose their strength as they expand. Thus, long and heavy springs are required to provide the high pressure required to push the injection fluid through the skin. In order to load the springs, it is necessary to use hydraulic cylinders and associated equipment, which is bulky and expensive.
The object of the present invention is to at least partially alleviate the problems described hereinbefore by providing a jet injector which is portable, and which does not require any cumbersome auxiliary equipment